Photosynthesis Physiology Response Of Populus Euphratica And Populus Pruinosa To Water Stress

Drought is the main reason causes big area deterioration of P.euphratica and P.pruinosa natural forest which maintain the survival depending on ground water. In order to discuss the mechanism on photosynthe -sis physiology response of P.euphratica and P.pruinosa under water stress, photosynthesis and chlorophyll fluorescence parameters of two years old seedlings under nomal water treatment (soil moisture content for field capacity 70%-80%),moderate water stress (50%-60%),and serious water stress (30%-40%) were measured,and adult trees under underground water level 4m,2.5m and 1.5m. The conclusion shows:(1) Under serious water stress,Gs,Pn,Pmax,LSP,AQY,Fv,Fv/Fm,Fv/Fo,qP,ΦPSII,ETR of two species reduce -d obviously,but LCP,NPQ and WUE rose,Which indicated serious water stress has affected photosynthetic capacity and PSII photochemical activeness seriously,and aggravated photoinhibition of P.euphratica and P.pruinosa.(2) After a period of drought training,Pn,WUE,Fv,Fv/Fm,Fv/Fo and qP of two species between moderate water stress and nomal water treatment didn't occur noticeable differences.It indicated that moderate water stress has not had the extremely serious influence on photosynthetic physiology function of two species.On the contrary, to some extent,could stimulate physiological regulatory function,also improve water use efficiency and its adaptability to the arid environment.(3) During the course of water stress, along with the extension of coercion and the intimidation of the deepening,the Pn of P.euphratica and P.pruinosa experienced three phases:sharp decline-slow, rebound -down and again under moderate and serious stress condition.16 and 24 days later after water stress starting,the reason of Pn drops mainly is the stomatal limit,and 48 days later,primarily is non-sto matal limit.Daily variation pattern of Pn,ΦPSII and other photosynthetic physiology parameters of P.euphra -tica and P.pruinosa have had a degree of change.(4) Living in different underground water level condition,the photosynthesis and PSII photochemical activeness of two species have significient difference.Along with the drop of underground water level,Pn, WUE,QUE,qP andΦPSII droped also.But the highest Fv,Fv/Fo and Fv/Fm appeared on 2.5m and 1.5m underground water level,and the lowest was 4m.It showed that the underground water level is the key ecological factor affect photosynthetic physiology condition of P.euphratica and P.pruinosa natural forest vegetation.When underground water level surpass 4m,the photosynthetic physiology function of P.euphratica and P.pruinosa will produce inhibition effection.(5) Whether seedlings or adult trees under identical habitat but different soil moisture,photosynthesis physiology parameters including Gs,Pn,Pmax,WUE,LSP,AQY of P.euphratica is obviously higher than P.pruinosa,but LCP is actually lower.under normal water condition,P.euphratica and P.pruinosa's Pmax respectively is 31.24,18.19μmol·m-2·s-1,AQY respectively is 0.054,0.038μmolCO2·μmol-1photons,LSP respectively is 610,551μmol·m-2·s-1,LCP respectively is 29,39μmol·m-2·s-1.Under drought condition, Daily dynamic change scope of P.euphratica kept gentle throughout,but P.pruinosa has larger fluctua -tions.The above result indicated:compared with P.pruinosa,P.euphratica has the higher luminous in tensity adaption scope and the photosynthetic physiology function,thus it can use the soil water more sufficiently,and be more suitable for Tarim River basin arid wilderness ecological environment with sufficient optical radiation,high temperature and few precipitation.